All 1970-74 E Body are the same size (the smaller size) . The larger ones are for B & A Bodies.
The two prong passenger side one is available anywhere, don't worry about the length...they're self adjusting.
The three prong driver's side is only available in used or NOS, as far as I know, with the NOS ones being harder to find these days.
Reproduction stuff has been coming out so fast I can't keep up, so who knows, they may be available now.